Cancer ranks as the first cause of premature death in many countries, a trend that is becoming similar in middle- and low-income countries. Currently, all therapies available fail to address several cancer conditions efficiently, and an appropriate treatment to prevent the development of metastases, which is the deadliest cancer feature, is still unavailable. Nearly 50–70% of all tumors are treated with platinum-based compounds. Due to noxious side effects caused by these metallodrugs and especially to resistance phenomena (innate or acquired), complexes with non-platinum metal ions have been explored for their anticancer properties. In this context, ruthenium-based metallodrugs emerge as prospective candidates for drug development showing, in some cases, concomitantly low toxicity, selectivity toward tumor tissues and inhibition of metastasis development. In this PhD thesis, structural diversity was rationally designed for two fragments containing the ruthenium ion stabilized in the +2 oxidation state by: i) a cyclopentadienyl family (‘RuCp’, [Ru(Cp)(bipy)(P)]+) or ii) a polypyridyl family (‘Ru(NN)2’, [Ru(NN)2(bipy)]2+). In either fragment, the consecutive modification at different positions of each building block (i.e., cyclopentadienyl (Cp) or N,N-heteroaromatic (NN), bipyridyl (bipy) and phosphane (P) ligands) alongside inclusion of biotin via esterification was achieved with success. In total, 49 new Ru(II) complexes were synthesized and fully characterized using several spectroscopic and analytical methods. The biological potential of the new compounds was assessed using lung, breast, and colorectal cancer cell lines. A series of in vitro experiments and molecular docking calculations were performed to establish structure-activity relationships and investigate features of cancer multidrug resistance. These studies included several key assessments, including (photo)cytotoxicity, cell death analysis, intracellular distribution, among others. Several Leads for cancer MDR therapy were identified. Proof-of-concept for one Hit structure was achieved in vivo on a mice model bearing non‑small cell lung cancer orthotopic tumors, where its low toxicity and efficacy on primary tumors was remarkable, validating in vitro results.